CpuStatsCollector

Helper class which runs cpustats continuously on an ITestDevice and parses the
output.

Provides a method to record the output of cpustats and get all the cpu usage measurements
as well methods for performing calculations on that data to find the mean of the cpu workload,
the approximate cpu frequency, and the percentage of used cpu frequency.

This is meant to be a replacement for TopHelper, which does not provide stats about cpu
frequency and has a higher overhead due to measuring processes/threads.

The cpustats command was added in the Jellybean release, so this collector should only be
used for new tests.